Multi-layers of xcexa-Al2O3 and Ti(C,O) or xcexa-Al2O3 and TiN have proved to exhibit better wear properties than single oxide layers, see U.S. Pat. No. 5,700,569 and U.S. Ser. No. 09/717,006.
The deposition process of these prior art multi-layers is, however, relatively long and deposition is usually carried out at relatively high temperatures (usually at about 1000xc2x0 C.), resulting in the transformation of kappa-alumina to alpha-alumina. The volume shrinkage encountered in the phase transformation will reduce adhesion of the alumina layers. As a result, adhesion problems in production will occur.
It has usually been thought that deposition temperatures of about 1000xc2x0 C. or higher are needed to deposit Al2O3 coatings. As shown in the recent U.S. application Ser. No. 09/498,344, Al2O3 can be deposited at the deposition temperatures about or exceeding 800xc2x0 C., but less than 1000xc2x0 C. Further, it was shown that the two Al2O3 phases, xcexa and xcex3, could be deposited in a controlled way.
It has recently been confirmed that Ti(C,N) exhibits better wear resistance against crater wear and flank wear in hypoeutectoid steels than TiN (U.S. Ser. No. 09/207,687). In recent in-house cutting tests, it has also been found that in hypereutectoid steel, Ti(C,N) is better that TiN, especially with respect to flank wear. In hyper-eutectic steel, Al2O3 is a superior coating material against crater wear. In recent cutting tests in-house, it has also been found that the adhesion of both xcexa and xcex3 phases to the MTCVD Ti(C,N) deposited at 800xc2x0 C. is surprisingly good. By depositing xcexa or xcex3 with MTCVD Ti(C,N) as a multi-layer, the wear properties of the prior art TiN/Ti(C,O)-xcexa multi-layers could thus be enhanced.
It is an object of this invention to avoid or alleviate the problems of the prior art.
It is further an object of this invention to provide enhanced wear properties of TiN/Ti(C,O)-xcexa multi-layers by depositing xcexa or xcex3 with MTCVD Ti(C,N) as a multi-layer.
In one aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of xcex3-Al2O3.
In another aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of xcexa-Al2O3 and/or xcex3-Al2O3 layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N).
In another aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of xcexa-Al2O3 and xcex3-Al2O3, each applied by a chemical vapor deposition at a temperature of from 700 to 900xc2x0 C.
In another aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of xcexa-Al2O3 and/or xcex3-Al2O3 layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N).
In yet another aspect of the invention there is provided a coated body wherein the coated comprises a multi-layer of xcexa-Al2O3 and/or xcex3-Al2O3 layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N) and with a layer of Ti(C,N) atop of the said multi-layer.